Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEY), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit battery) of the middle- or large-sized battery module. Especially, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
Battery cells constituting such a middle- or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. In particular, the laminate sheet of each pouch-shaped battery widely used in the battery module has a polymer material exhibiting low thermal conductivity coated on the surface thereof, with the result that it is difficult to effectively lower the overall temperature of the battery cells.
If the heat, generated from the battery module during the charge and discharge of the battery module, is not effectively removed, the heat accumulates in the battery module, with the result that deterioration of the battery module is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
Each battery module mounted in a middle- or large-sized battery pack is generally manufactured by stacking a plurality of battery cells with high integration. In this case, the battery cells are stacked in a state in which battery cells are arranged at predetermined intervals such that heat generated during charge and discharge of the battery cells is removed. For example, battery cells may be sequentially stacked in a state in which the battery cells are arranged at predetermined intervals without using an additional member. Alternatively, in a case in which the battery cells have low mechanical strength, one or more battery cells are mounted in a cartridge, and a plurality of cartridges are stacked to constitute a battery module. In order to effectively remove heat accumulating between the stacked battery cells or between the stacked battery modules, coolant channels may be defined between the stacked battery cells or between the stacked battery modules.
In this structure, however, it is necessary to provide a plurality of coolant channels corresponding to the number of the battery cells, with the result that the overall size of the battery module is increased.
Also, coolant channels having relatively small intervals are provided in a case in which a plurality of battery cells are stacked in consideration of the size of the battery module. As a result, design of the cooling structure is complicated. That is, the coolant channels have relatively small intervals as compared with a coolant inlet port, with the result that high pressure loss is caused. Consequently, it is very difficult to design the shape and location of a coolant inlet port and a coolant outlet port. Also, a fan may be further provided to prevent such pressure loss. In this case, however, design may be restricted in terms of power consumption, fan noise, space, etc.
Meanwhile, for plug-in hybrid electric vehicles or electric vehicles, which have recently become a focus of attention, a battery pack requires power corresponding to acceleration performance generated by an internal combustion engine. As a result, very high current may flow in the battery pack for several minutes. In this case, high-temperature heat is generated from electrical interconnection regions between the battery cells, and such heat affects the battery cells through thermal conduction. For this reason, it is necessary to configure the battery module in a structure in which such heat is controlled.
Also, in a case in which high-temperature heat is generated from the electrical interconnection regions due to high current, it is necessary to control the electrical interconnection regions. However, using a method of cooling the battery cells or providing an active cooling device to control the temperature of the electrical interconnection regions is not effective in terms of space or costs.
In addition, a conventional middle- or large-sized battery module used as a power source of hybrid electric vehicles uses temporarily high current. However, the internal combustion engine is a main power source, and the battery module is an auxiliary power source, with the result that use time at high current is very short, and therefore, heat sufficient to affect the battery cells is not generated. For this reason, an additional structure or method for cooling the electrical interconnection regions is not considered.
Consequently, there is a high necessity for a battery module that provides high power and large capacity and that is capable of effectively reducing heat generated from electrical interconnection regions between the cells, thereby providing excellent life span and safety.